1. Field of the Invention
The invention relates to a method and a machine for notching a tube such as a headrest frame tube of a seat of a motor vehicle.
The invention applies in particular, but not restrictively, to height-adjustable headrests the frame of which consists of two parallel legs, at least one of which includes a plurality of notches, each defining a height-adjustment position of the headrest and an end notch forming a positive stop opposing an involuntary extraction of the headrest out of its guides when it is pulled upwards, except after a voluntary unlocking. In order to retain the headrest, these notches cooperate with latches integrated into guiding sleeves provided at the top of the seat back.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Different notch profiles are shown in FIG. 1. Some notches 11, 12 comprise a steep locking flank and a sloping flank, other notches, for example, the end notch 13 shown in detail in FIG. 2, comprise two steep locking flanks and a flat bottom.
The locking flanks must be as steep as possible, even on slopes (or undercuts), they must form an angle as sharp as possible with the outer surface of the wall of the tube, they must be as less wide as possible and as deep as possible, in order to guarantee the impossibility of inadvertently unlock the headrest.
On solid metal rods, these notches are easy to be produced, regardless of their profile, by machining or cold deformation (stamping). But in order to reduce the weight of the headrest frames, one seeks to make tubular frames and producing a notch on a tube by means of transverse deep-drawing inevitably causes a sagging 41, 42 of the outer wall of the tube (FIG. 4). This deformation does not permit to obtain the desired sharp angles for the transverse flanks of the notches in order to make impossible an inadvertent unlocking of the headrest. This deformation in addition leads to a local increase of the diameter of the tube, which disturbs the sliding of the tube in the guiding sleeve.
Document FR 2 842 752 discloses a method and a notching press for producing notches with transverse flanks on a tube. The use of a specific mandrel inside the tube, into contact with the wall of the tube, permits the material hammered by the punch to move to the inside of the tube, which prevents the local increase of the diameter of the tube. This solution permits to produce notches with one or two transverse flanks, even small-width notches. But this technical solution does not permit to obtain the desired sharp angles for the transverse flanks of the notches; neither does it permit to produce notches with a depth larger than the thickness of the wall of the tube.
FR 2 816 857 discloses a method and a notching punch permitting to produce notches with one or two transverse flanks on the tube. The use of a punch in a direction inclined by about 30° permits steep flanks with a sharp edge. But, due to the inclination of the punch, the width of a notch is necessarily much larger than the width of the punching tooth and it is not possible in practice to make small-width flanks, including namely notches with double transverse flanks.